1. Field of the Invention
The invention is directed to a device for the block-by-block conversion of a first digital block into a second digital block using at least one freely selectable control block, each of the blocks having an equal number of digits.
2. Description of the Related Art
Transmission networks using the Data Encryption Standard DES have been in use throughout the world for more than ten years. This DES standard of the American National Bureau of Standards (NBS) is used for block encryption with individually selectable keys (secret key block encryption). Every plaintext block has a length of 64 bits, as does the ciphertext block. A sequence of 64 bits, 56 of which can be freely selected, serves as key (secret key). The transmission of the ciphertext block is effected via a public network.
In general, the Data Encryption Standard DES is a very good encryption tool. However, it is an open, debatable question whether or not the DES Standard has failed to remain secure in the meantime. The small length of the secret key plays an important role in this.